Not So Fast, Neutrinos!

Researchers reported this week that the extraordinary faster-than-light neutrinos that turned up in a European experiment last year could have been the result of a simple wiring glitch. Einstein may be vindicated yet again if the faster-than-light report was false. But here's why neutrinos could still carry plenty of secrets about the early universe.

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A few months ago, subatomic particles called neutrinos zipped through the news faster than the speed of light, supposedly breaking the universal speed limit, toppling Einstein in the process, and igniting arguments among physicists everywhere. It turns out, however, that those extraordinary results might have a rather mundane explanation: a glitch in the wiring of the experiment.

The official statement from CERN says that the team behind that experiment identified two different problems that could have affected the timing of the experiment, one that would have overestimated the time, and one that would have underestimated it. The team now says it plans to re-run the tests in May. Meanwhile, other groups around the world will try to re-create the experiment over the course of the next year.

The argument isn't over. The physics community is still puzzling over the aftermath of the results released last September. Neutrinos are a big deal in particle physics and could hold the answers to very large questions about how the universe works.

Law-Breaking Particles

"Neutrinos turn out to be a very weird form of matter that we're still trying to figure out," Robert Svoboda says. Svoboda is a physicist at the University of California, Davis, who studies how neutrinos work. He says that while he remains skeptical of the original results, he and others in the community were intrigued by the idea that neutrinos could travel faster than light. "People were willing to give it the benefit of the doubt because they [neutrinos] seem to break other physical laws," he says.

For instance: Scientists know that neutrinos come in three types: electron, muon, and tau. Other, larger subatomic particles, such as quarks, also come in three varieties. But unlike those quarks, neutrinos have the weird ability to transition between these forms as they travel through space, and researchers are still trying to figure out how or why.

That was the intended purpose of the experiment in Italy last fall: to catch neutrinos in the act of breaking the law by changing their type on the fly. To that end, researchers at the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) shot a beam of muon neutrinos from CERN headquarters in Geneva to Gran Sasso, Italy, a little over 450 miles away. The Gran Sasso National Laboratory is the largest underground lab in the world, situated under nearly 4600 feet of rock. The rock blocks out the irritating cosmic radiation found on the Earth's surface, allowing scientists to study subatomic particles without interference.

They had hoped to see some tau neutrinos appear on the receiving end, demonstrating that the particles could shift while in transit. The experiment did catch some tau neutrinos, but one day it caught something more exciting: neutrinos arriving 60 nanoseconds earlier than they were supposed to.

Physics Showdown

Sixty nanoseconds (a nanosecond is one billionth of a second) don't seem like much to us, but that time difference is incredibly important to physicists who work under the Einstein-based theory that nothing can travel faster than the speed of light in a vacuum. Finding something that traveled faster than light would require a re-writing of textbooks and some changes in experimental physics.

Svoboda says that while many theoretical physicists were seriously questioned the results, the experimental physicists he talked to have been a bit more circumspect, wanting to get more information from other experiments. "We've seen things that we think are absolutely right turn out to be wrong, and vice versa," he says. Future experiments, both at OPERA and other locations in the U.S. and Japan, should help to prove or disprove the results.

As for a faulty wire messing up the timing measurements? It's certainly a plausible explanation. "It takes electrical signals and light signals time to travel through a wire" Svoboda says. Researchers have to account for that tiny lag time by knowing the length of all the wires in a system and adjust their findings to get an accurate result.

Even without a wire problem messing with the timing, tracking neutrinos is extremely difficult. They rarely interact with matter; billions are zooming through your body right now. To spot neutrinos, the scientists at OPERA have to work with a huge detector made of 150,000 bricks of a photographic film, separated by lead sheets and stacked into large walls. If the equipment tells the scientists that they've got a neutrino interaction, they can then take the bricks out of the wall and develop them as they would camera film.

Secrets of the Universe

Neutrinos have more to offer physicists than potential speed-limit-defying stunts. Svoboda and others are trying to unravel the particles' enigmatic behavior because neutrinos could explain why the universe looks the way it does.

One of the big unanswered questions in physics is, to be blunt, why enough matter exists to form stars, galaxies, planets, and even puny humans. Matter and antimatter annihilate each other on contact and theory would suggest that equal parts of both existed after the big bang, yet here we are in a matter-based universe. Svoboda thinks that perhaps neutrinos shifted the balance between matter and antimatter soon after the big bang.

Most particles have a corresponding antiparticle (quarks and antiquarks, hydrogen and antihydrogen), and neutrinos do too, but antineutrinos behave very differently from other antiparticles. Specifically, antineutrinos spin only to the right and neutrinos spin to the left, while in other matter–antimatter pairs the spin would be the same in both. Researchers are trying to figure out if this discrepancy in behavior means that neutrinos can actually transform antimatter into matter. If this is the case, they could have interfered just enough to allow more matter than antimatter to survive.

It's a cool theory, but in order to prove it, scientists first have to figure out how neutrinos work and how exactly they would interact with the rest of the particles in the universe—no small order. Svoboda is one of the leading scientists on a future project, the Long Baseline Neutrino Experiment (LBNE) which would stretch from Fermilab near Chicago to the South Dakota/Wyoming border. The LBNE would be similar to the Gran Sasso experiment in Italy—scientists would fire neutrinos from Fermilab toward the detector in South Dakota. "We would look to see if the right- and left-handed neutrinos would interact [so that] one was producing more electron neutrinos than the other type," Svoboda says.

It's a mystery that won't be answered for at least another decade, when the LBNE should be complete. That's a long time to wait, but for some physicists, the magnitude of the potential discovery makes the wait worthwhile. "If you were a biologist and you'd only ever seen plants, it would be like seeing an animal for the first time" Svoboda says. "That's why people are interested in studying them, there's no telling what other weird stuff they do."